I have just recently bought a 27 gallon aquarium. Before I had 5 black skirt tetras, 2 guppies, and 1 neon tetra in a ten gallon aquarium. Before transferring my old fish into the new aquarium, I bought 2 more b.s.t and a Lyretail Molly. 2 days after putting in the molly, she died. The molly would just lay on the bottom and rarely eat, she was also pregnant. Three days later I found one of my guppies stuck on my filter. When he was rescued, I noticed his back fin was torn. 2 minutes later he went back in the same spot and got caught again. After 3 minutes of him being rescued and getting caught again, he started to float vertically pointing straight up. The next morning I found him dead My other guppy is acting fine and looks great. What is killing my fish?

I bought a new filter that is big enough for my tank. Before adding my fish I had put water conditioner in the aquarium along with aquarium salt. I still have 9 fish in the aquarium and they are doing fine. Is ammonia or nitrate poisoning still the cause of death, and if so why has it only killed 2 of my fish?_________________INEEDMORETANKS!!!!!

You other fish haven't died yet.
The filter works by using bacteria to break down fish wastes. A new filter doesn't have these bacteria so the toxins build up. Some fish succumb sooner than others. Your old filter would have supported the fish you moved.
You need to do daily 30 -40% water changes and it would help if you got liquid test kits for ammonia, nitrite & nitrate.

I added the amount of which the container said to which was 1 tablespoon for every 5 gallons. Would the 30% water changes save the fish? Is their any other way I could help the tank. Both nitrates are at 0._________________INEEDMORETANKS!!!!!

At this stage it is probably ammonia - nitrItes follow & then nitrates.

Water change are best course of action unless you know someone with a mature tank who could donate so filter bacteria - either used media or filter squeezings?

Helping fish through a nitrite spike is one time that aquarium salt is useful but your mollies will appreciate it and the tetras won't.
A tablespoon per 5 gallons is a high dose - molly amount not tetras.
Try the tests again but shake the bottles a few more times.

I use testing strips instead of actual water testing. Could I get the water testers at petsmart? I have an Uncle who has an established aquarium. How would I get the bacteria into my water?_________________INEEDMORETANKS!!!!!

Get some of the water from his filtration system and add it to your filtration system. Could jump start your colony. If it was me, I'd ask for 32 oz (a large plastic drink from McD's) and add it fresh from his filter.

Test strips are notoriously unreliable and ammonia is the current problem.

If you can get your uncle to take some sponge or filter media from his filter & swish it around in a poly bag of tank water - basically the same as clearing his filter. Treat this mucky water as if it contained fish and tip it into your tank near the filter intake. (or into your filter if it is HOB).